Unit 3: Acids, Bases, and pH

What is the range of the pH scale from lowest to highest?

0-14

Water has a pH of ______ and is said to be __________.

7, neutral

Suppose that you were given a sample that had a pH of 6.5 but you were unaware of the pH. a. Can you perceive a problem that would arise if you attempted to determine the pH of this sample using either anthocyanins or pH paper?

A problem that would arise is that the pH paper would not be accurate enough and would most likely read a 7 instead a 6.5.

Which common substance is a base

Ammonia

1 out of the 3 ways used for measuring pH - advantages/disadvantages

Anthocyanins (cabbage extract) Advantage: they change color in response to changes in pH. These pigments are responsible for red, blue, and purple colors that are found in flowers, fruits, and autumn leaves. Disadvantage: slower process than litmus paper, contaminates solution, does not tell the strength of an acid, more solution required than litmus paper, if it's a dark solution you cannot see the color change.

A solution with a pH of 8 is ___________.

Basic

Know the color that a buffer appears at a low pH, high pH, and neutral pH when anythocyanins are used.

Color with anthocyanins - Low pH: Hot Pink -Neutral pH (7) Indigo High pH: Green

b. is the use of a pH meter qualitative or quantitative?

It would be quantitative.

A measure of the power of the hydrogen ion concentration in a solution is pH 7 is neutral, lower values are more acid, and higher values more alkaline.

PH

a. Is the use of anthocyanins qualitative or quantitative?

Qualitative measures, because an anthocyanin color Is strongly dependent on the pH.

Anthocyanins were extracted from what?

Red Cabbage

Terri needs to determine if an unknown substance is an acid or base, so she puts on safety goggles and gloves then cuts a strip of pH paper. She places a drop of the unknown substance on the pH paper and reads the results within 5 seconds. The bright red color indicates a pH of 2, so the unknown substance must be a base. Terri made a mistake! What was her mistake?

Terri is confused about pH numbers - A reading of 2 means it is an acid.

Be able to read a graph to determine which solution has the greatest buffering capacity and why.

The one that is super high doesn't have a buffer and the one that has a neutral response has a buffer

. What about using a pH meter?

There is no issue with using the pH meter.

Acids with a low pH and bases with a high pH are considered very dangerous.

True

An substance which donates a proton. (Loses a Hydrogen Ion)

acid

plant pigments that can be used as a pH indicator because they change color in response to changes in pH.

anthocyanins (pigment)

Any substance which accepts a proton. (Gains a Hydrogen Ion)

base

special solutions that can help maintain pH by resisting any changes to pH caused by the addition of an acid/base.

buffer

What was the base that was used in the lab?

detergent water

3 out of the 3 ways used for measuring pH -advantages/disadvantages

electronic pH meter: 1. Confirm that the meter is on the pH measurement mode. 2. Thoroughly rinse the pH electrode between measurements with distilled water to prevent carryover contamination of the tested solutions. ... 3. Dip the pH electrode into a testing solution or suspension. ... The pH is completed when the pH reading is stable. advantages: they measure more accurately than a test strip or other method of pH measurement Disadvantage: Deposits on the electrode membrane can interrupt the processes. The pH meter is often needed to calibrate. The special buffer solution is required to calibrate it. The pH calibration may be influenced by temperature and carbon dioxide absorption. There is a possibility of breaking due to fragile glass electrodes.

What is the pH value of a solution based on?

hydrogen ion concentration

A liquid is considered a base if it has a lot of _________.

hydroxide ion

A solution has a ____ buffering capacity when it easily changes pH after adding an acid or base.

low

Would you have been able to determine the pH of the three unknowns using the cabbage juice if you had not made your standards (the test tubes containing each of the buffers and the cabbage juice)? Yes or no.

no,without standards it is not able to know what the actual color change will become.

Which measurement METHOD would you consider to be a most reliable measurement?

pH meter

Which measurement would you consider to be a most reliable measurement; anthocyanins, pH paper or pH meter?

pH meter

2 out of the 3 ways used for measuring pH -advantages/disadvantages

universal pH paper (7,Neutral,Green) advantages: They are cheap, rapidly produce a result that is good to about a pH unit and can simply be discarded after use. Disadvantages: If you want you want numbers more accurate, too bad. Also, they are single use so not good for continuous measurement

What acid was used in the lab?

vinegar